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Building a House - Theoretical Studies

"But,"continued Eugene,"your bay windows project too far to allow of their resting on corbelling." "What do you mean by corbelling?" "It is a projecting piece of construction, not rising from the bottom, but supported by corbels; whence the name corbelling. The weight of the masonry resting on the tail, i.e. the part of the corbels fixed in the walls, allows us to place on their projecting part a construction, which, being less heavy than that resting on their tail, is thus sustained without fear of overbalancing. We must also calculate the length of the arm of the lever - that is to say, the relation of the projection of the corbels to the weight that secures their tail and that which rests on their head. Of course, the further the corbels project the more does the weight placed on their outward extremity tell on that which keeps the balance. So that a very trifling weight placed at the extremity of a greatly projecting corbel might overbalance a heavy mass placed at the tail. Corbels have, therefore, been frequently replaced by squinches - that is to say, a system of masonry which brings the weight at the extremity to bear on the walls. The architect who designed the oriel window I have just shown you did not trouble himself to make such an arrangement. He constructed what is called a bracket - that is, an inverted pyramid, by means of three courses of corbelling; or, if you choose, projecting one beyond the other, so as to obtain a portion of a polygon. On this supporting surface he has erected his window framing, which is scarcely 91 inches thick. The bracket being built into the wall, supports the window framing, without being over-balanced, on account of the weight of the wall. Closed balconies of this kind were frequently employed during the Middle Ages, because they gave space in the upper stories without encroaching on the street, and afforded side views. And though civic regu lations no longer allow us to build these projections in our cities, nothing would hinder us from erecting them when we build in the country. Still, there ought to be a good reason for adopting them. And in our case these corbel constructions serve no purpose, and it will cost us less to raise our bay window direct from the ground." In about an hour Eugene handed to Paul the accom panying sketch (Fig. 44), giving the arrangement of the bay window of the billiard-room, that he might study its construction. It required a good deal of, attention from our clerk-of-works, and he could not master it thoroughly without frequently applying to his cousin for information and explanation.

The weather becoming more and more severe prevented the works from being resumed. The parts that had been begun were hidden by a thick layer of mould and stubble, which in its turn was covered by a mantle of snow. The days were spent in working out details which were to be given to Branchu and the carpenter when the weather allowed them to resume their labours. During the long evenings, theoretical questions relating to building were dis cussed, when the family were assembled and the news of the day had been read. To Paul this was a means of gaining instruction, and to the family generally a distraction from the gloomy thoughts that weighed down the spirits of all amid the depressing circumstances of the times. Paul had seen his cousin drawing several mouldings during the day, to their full size; but as he had drawings of his own to attend to, he had not interrupted his work to put questions to his master. But in the evening Paul asked what were

the methods to be employed in drawing these mouldings.

"You still persist in asking for recipes, Paul,"replied Eugene."But there are no more any recipes for drawing mouldings than for any other parts of the building. There are conditions imposed by the purpose, the nature of the materials, the method of employing them, local custom, and the effect to be obtained. To the consideration of these conditions join common sense, observation, and study, and you will be able to draw mouldings.

"We will, if you please, examine these conditions separately.

"The purpose : - A moulding is executed, you must sup pose, for some object; if you draw a cornice, it is to crown a wall, to carry a gutter or the eaves of a roof, to divert the rain-water from the wall; that cornice- therefore must project sufficiently to fulfil that object. - The nature of the materials : - It is evident that if you have, on the one hand, hard and tenacious stones, supplied in large masses, or, on the other hand, small and friable ones, you will not be able to give the same profile to these different kinds of materials. - The method of employing these stones must likewise influence the form to be given to this profile. If we have to hoist stones by the aid of very simple and primitive means, which do not allow us to raise con siderable weights to great elevations, we must avoid profiles requiring large blocks; but if we have the means of doing so, we can adopt them. - Local custom : - It will be neces sary for you to take account of the customs of the district in which you are building, because these customs are most frequently the result of a judicious observation of the con ditions imposed by the climate, the requirements of the neighbourhood, the method of working, and the nature of the material itself. I mean by custom, not certain imported methods which are a mere affair of fashion, but those which have been suggested, as I have just said, by long and judicious observation. - A skilful architect can give a robust or a delicate aspect to a building by the drawing of a moulding. He should always subordinate the drawing to the scale of the construction and to that of the materials. It is ridiculous to aim at large mould ings if we have only thinly bedded stones, or those of yielding quality, in the same way as it is absurd to give delicate profiles to coarse stones and those difficult to cut.

"You see, then, that in this, as in all that concerns the art of building, reasoning constitutes the first part of the recipe.

"The Athenians, who erected their public buildings of white marble, could allow themselves refinements in the drawing of their profiles which cannot be applied to the coarse limestone of our country. And when the Greeks built edifices with stone of a porous or coarse-grained texture, they took care to cover its dressed surfaces with a very fine stucco, which enabled them to conceal the coarseness of the material. But though they were able to adopt this plan in a mild climate where it never freezes, it would be impracticable in a region like ours, where for two months in the winter the thermometer shows a mean of 7° (Fahr.) below freezing point, and occasionally, as just now, falls as low as 27 below freezing. This stucco would have to be renewed every spring.

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drawing, weight, corbels, stones and window